Magnetic structure



Oct. 11, 1932. H. LATHROP 1,881,711

MAGNETIC STRUCTURE Filed Aug. 1 4, 1931 //v l ENTOR h. LA THROP I whole.

Patented Oct. 11, 1932 UNITED STATES PATENT OFFICE HUIBBEL LA THROP, OF GREENWICH, CONNECTICUT, ASSIGN OR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK MAGNETIC STRUCTURE Application med August 14, 1931. Serial No. 556,951.

This invention relates to magnetic materials and magnet cores, and more particularly to magnet cores for loading coils for telephone circuits and to their method of production.

The principal object of the invention is to produce a magnetlc element which has low core losses and a relatively high permeability and which possesses to a high degree the electrical'and magnetic characteristics that are desirable in electrical signaling apparatus generally and in loading coils for telephone circuits particularly.

The present invention, in one of its embodiments, is applied to the construction of magnet cores comprising fine particles of a nickel-iron alloy bound together with a suitable insulating material and heat treated to have a higher inherent magnetic permeability and lower inherent hysteresis loss than iron. More specifically the invention is directed to the formation of magnet cores of a nickeliron alloy in finely divided form in which 25% of the alloy comprises nickel and the remainder principally iron, the nickel content in one form which has proven satisfactory being approximately 78 of the The metal articles are mixed with a binding materia such as kaolin, and treated with a colloidal solution formed by adding'a solution of an organic salt, such as chromic acetate, to a solution of sodium silicate. The whole is evaporated to dryness with constant stirring, leaving a coating on the metal particles. The coated particles are then pressed into cores of the desired size and shape. The cores so formed are finally heat treated at the optimum temperature for the particular alloy of which the cores are constructed, whereby the organic material left by evaporation IS dIlVBII off and a supplementary insulation is formed, which comprises chiefiy the oxide of the metallic element of the organic salt which remains. The heat treatment gives the allow a high permeability, low hysteresis losses and high specific resistance, and hence results in low eddy current losses in the cores.

The nature of the present invention will more fully appear in the following detailed description of a specific embodiment thereof.

The single figure of the drawing is 8. erspective view of a loading coil core ma e in accordance with the present invention. It will be understood, however, that this is merely illustrative and that the invention is not limited to the roduction of this form of core but is adapte to the production of cores of magnetic particles in many forms' In carrying out the present invention, the magnetic material employed is preferably prepared from a nickel-iron alloy commonly referred to as permalloy, which is treated in a manner more fully described in U. S. Patent 1,669,649, issued May 15, 1928 to C. P. Heath and H. M. E. Heinicke, to reduce the alloy to a finely divided form. Experience has proved that where low eddy current losses are desired, it is essential that the particles be of small size and preferably of such size that all of them readily pass through what is generally known as a 120 mesh screen and that a large percentage pass through a 200 mesh screen. According to one embodiment of the invention, the alloy is prepared by melting approximately 78 parts of nickel and 21 parts of iron in an oxidizing atmosphere and pouring the resulting alloy into a mold. When prepared according to the foregoing process, the resulting alloy .is exceedingly brittle, and it is therefore particularly adapted to be reduced to a finely divided or dust form from which the finished cores are molded.

After the brittle ingots are obtained, the are successively passed while hot throu progressively reducing rolls which form t e alloy into flat slabs approximately one-quarter of an inch thick. By the hot-rolling process the size of the crystalline structure is materially reduced, which, since the disintegration of the material takes place mainly at the crystal boundaries, is essential -in order to have a satsfactory yield of dust. The rolled slabs are broken into short pieces and are then further reduced by crushing in a jaw crusher, hammer mill, or any other suitable type of apparatus. The material after being passed through the aw crusher is subsequently rolled in a ball mill until it is reduced toa l fine dust. The dust is then assed through a 120 mesh sieve. Any resi ue is remelted and the foregoing operation is repeated to again reduce the material to a finely divided form. Prior to the addition of the insulating material, the finely divided particles of the nickel-iron alloy are annealed in a closed container at a temperature of from approximately 750 C. to 980 C., a. temperature of about 925 C. producing very satisfactory results. It is then necessary to again reduce the annealed allo which is now in the form of a cake, to a nely divided form, after which it is mixed with the insulating material.

According to one form of the invention, the materials are prepared as follows. With every 100 parts by weight of the magnetic particles, 1.1 parts of kaolin'and 0.4 parts of talc are mixed dry. To 1.15 parts of sodium silicate dissolved in water are added 0.115 parts of chromic acetate in the form of a 5% aqueous solution. This latter combination results in a colloidal silica sol, which is then added to the mixture of magnetic particles and binding material and thoroughly stirred therewith. The entire mass is then evaporated to dryness, accompanied by constant stirring to prevent caking and to insure a complete coating of the particles. After this process is completed, the coated dust particles are in a form suitable for ressing into cores or rings. These latter are preferably formed under a pressure of approximately 200,000 pounds r square inch. A high pressure is used in orming the ring in order to increase their density, since it has been found that the permeability of the cores increases with increase indensity. Finally the cores are transferred to an annealing furnace where they are annealed, preferably at a tempera- .ture of from approx1mately4'70 C. to 850: O.

- The temperature and duration of this process is'sufiicient. to break down and drive off the organic component of the residue left by evaporation. At the same time the metallic -component of the organic salt originally present is converted to the oxide, which remains as an insulating layer supplementing that due to the silica gel left by the evaporation of the colloidal silica solution. Except for the requirements of the annealing process, a temperature of 400 C. or less could be used to efiect these chemical changes.

In a pending application o f C. C, Neighbors bearing Serial No. 505,956, filed December 31, 1930, there is described an insulating material for finely divided magnetic particles that includes the end-products obtained by heating a. mixture of sodium s licate and an organic acid. In this case the peptizing agent;i i. e., the organic acid, is entirely remove by the heating process. A metal salt of an organic acid has the same peptizing effect as the acid, it is found, and at the same time it affords a substantial supplementary insulation due to the oxidation of the metallic component.

A plurality of the rings thus formed are stacked, as shown in Fig. 1, to form a core 2, to which the usual toroidal windings 1 are applied. The number of such rings used depends, of course, upon the existing electrical characteristics of the telephone circuit with which the loading coils are to be associated.

Although the permalloy particles have been described as insulated with a mixture of chromic acetate, sodium silicate, kaolin and tale in definite proportions, it is to be understood, of course, that the nature and proportions of the several ingredients may be varied without departing from the spirit and scope of the present invention. The, sodium silicate, for example, may be replaced with other e uivalent salts, such as sodium aluminate; either the kaolin or the talc may be used alone as the bindin agent or they may be replaced with such an oxide. The proportions will vary accord- I ing to the mechanical and electrical require?" ments of the finished cores. Other magneti alloys than the one specified may also be em ployed and the insulatin material selected may be adapted to the eat treatment required by the alloy.

Magnetic cores made in accordance with the method described herein are characterized by high permeability and low hysteresis. and eddy current losses, which are especially desirable electrical characteristics.

What is claimed is:

-1. As a new article of manufacture, a substance composed of particles of a magnetic material and an insulating material therebetween, said insulating material being made up of sodium silicate and a peptizing agent having a metallic and an organic component.

' 2. As a new article of manufacture, a magnetic substance composed of particles of a magnetic material, and an insulating material separating said particles made up of. sodium silicate, a metal salt of an organic acid and a binding material.

3. As a new article of manufacture, a magnetic substance composed of particles of a magnetic material, and an insulating mate.- rial comprising sodium aluminate, a metal Sill: of an organic acid and a binding materia 4. As a new article of manufacture, a magnetic substance composed of particles of a magnetic alloy of nickel and iron, and an insu lating material separating the particles comprising material such as sodium silicate or aluminate, a metal salt of an organic acid and kaolin.

5. As a new article of manufacture, a magnetic substance composed of finely divided particles of a magnetic alloy of nickel and iron, and an insulating material comprising sodium silicate, chromic acetate and a filler separating the particles.

6. As a new article of manufacture, a magnetic substances composed of finely divided particles of a magnetic alloy of nickel and iron, and an insulating material comprising sodium silicate, chromic acetate and a filler separating the particles.

7. As a new article of manufacture, a magnetic substance composed of finely divided particles of a magnetic alloy of nickel and iron, and an insulating material comprising sodium silicate, chromic acetate and kaolin separating the particles.

8. As a newarticle of manufacture, a magnetic substance composed of finely divided particles of a magnetic alloy of nickel and iron, and an insulating material made up of ten parts of sodium silicate and one part of chromic acetate, and a binding material, separating the particles.

9. As a new article of manufacture, a magnetic substance composed of finely divided particles of a magnetic alloy of nickel and iron, and an insulating material made up of ten parts of sodiumsilicate, one part of chromicacetate, and thirteen parts of filler separating the particles.

10. As a new article of manufacture, a magnetic substance composed of finel divided particles of a magnetio alloy, said alloy being composed of more than 25% nickel and the remainder principally iron, and an insulating material consisting of ten parts of sodium silicate, one part of chromic acetate, ten parts of kaolin and three parts of talc separating the particles.

. 11. A magnetic material comprising finely divided particles of a magnetic metal insulatcd with the end-products obtained b mixingand heating t erewith sodium sil1 cate, water and a decomposable peptizing agent having a metallic component whose oxide is highly non-conductive.

12. A. magnetic structure comprising par- .ticles of a magnetic material and an insulating composition coating said articles, said composition including'the en -products obtained by heating a mixture'of sodium silicate and a metallic salt or an organic acid to a temperature above 400 C.

13. The method of making magnetic structures, which comprises coating particles of a magnetic material with a mixture comprising sodium silicate and a metal salt of an organic acid, forming a mass of such coated particles into a homogeneous solid, and subjecting said solid to heat treatment, whereby said mixture is caused to change chemically to form an insulating binder between sald particles.

14. The method of making magnetic structures, which com rises reducin a magnetic alloy to a finely ivided form, Treat treating the finely divided particles, reducing the product so obtained to a finely divided form, coating the resulting product with a mixture including sodium silicate and a metallic salt peptizing agent, forming a mass of such coated articles into a homogeneous structure, and an insulating binder tween said particles.

15. -The method of making magnetic structures which comprises mixing'particles of magnetic material with a colloidal solution of a metallic salt of an organic acid and a water-insoluble insulatin material such as silica, dehydrating the mixture, and heat treating it to decompose its or anic constituents and to form a highly insu atingcoating on said particles.

16. The method of making magnetic structures which comprises mixin particles of a magnetic material with a co oidal sol comprised of a material such as sodium silicate and a metallic salt, dehydrating the mixture, and heat treating it to form an insulating materialfrom said metallic salt.

17. The-method of making magnetic structures which comprises mixing particles of a magnetic material with a material such as water glass and a metallicsalt of an organic acid, evaporating the mixture to dryness, and heat treating it to remove the organic component of sald salt and to form an insulating oxlile from the metalhc component of sai sa 18. The method of making magnetic structures which comprises combining solutions of sodium silicate and chromic acetate, mixing the resulting combination with finely di-' vided particles of an iron-nickel alloy, desolvating the mixture, forming said mixture in a homo neous solid, and heat treating it heat treatin said structure to form to drive 0 substantially all of the volatile con- I stitpents thereof, whereby a high degree of insulation between said particles is obtained and the magnetic characteristics of said alloy are' improved.

19. The method of making magnetic structures composed of finely divided .particles of an alloy consisting of more than 25% nickel and the remainder principally iron, which comprises mixing ten parts of sodium silicate, one part of chromic acetate in aqueous solution, and a binding material with said particles, drying said mixture, forming it, and heat treating it to improve the magnetic and electrical properties of the resultant structure.

'In witness whereof, I chereunto subscribe my name, this 7th da 0AA. ust, 1931.

1 fgLATHROP. 

